DLC is an amorphous carbon material having a property intermediate between diamond and graphite, and is called as a hard carbon, a hard amorphous carbon, an amorphous carbon, an i-carbon, a diamond carbon, or the like. The DLC has a high hardness with excellent wear resistance, solid lubricity, thermal conductivity, and chemical stability, like diamond. For example, the DLC is used as a protective film for a member requiring wear resistance.
Since the DLC film generally has a low adhesion to a substrate, however, an intermediate layer is formed between the DLC film and the substrate so as to enhance adhesion between the DLC film and the substrate. For example, Japanese Unexamined Patent Publication No. 2004-68092 discloses that an intermediate layer with a gradient structure between metal and carbon is formed between a DLC film and a substrate, thus improving the adhesion between the DLC film and the substrate. Further, Japanese Unexamined Patent Publication No. 2008-25728 discloses that an underlayer made of at least one kind of metal selected from the group consisting of Cr, W, Ti, and Si, and an intermediate layer made of the metal and carbon are formed between a substrate and a DLC film thereby to improve the adhesion therebetween. The total thickness of the underlayer and the intermediate layer is reduced to 1 μm or less from the viewpoint of enhancing the adhesion.
Thus, any one of techniques for forming the intermediate layer and the underlayer between the DLC film and the substrate serves to improve the adhesion between the DLC film and the substrate.
However, in the case of applying the technique to a sliding member to be used under a high pressure of contacted surface of 2.0 GPa or more, the above effect cannot be sufficiently obtained, which leads to reduction of durability.